The present invention relates to an automatic braking-gap adjuster system for a mechanical drum brake used with a light car etc., including a back plate, a pair of brake shoes each having one end pivotally supported thereon and a cam member interposed between both shoe web free ends of the shoes and extending through the back plate, said brake being designed to be put in operation by turning the cam member through a brake arm to expand the brake shoes and thereby urge them upon the inner periphery of a brake drum.
In the prior art automatic braking-gap adjuster system of such a type, a cam adapted to expand brake shoes by its rotation is sequentially regulated to a different angle of rotation with the progress of abrasion of linings to provide automatic adjustment of a braking-gap between the inner periphery of a brake drum and the surfaces of the linings. Accordingly, the amount of rotation of a brake arm needed for effecting sufficient braking increases with increases in the abrasion loss of the linings, leading to increases in the amount of rotation of the cam. This also results in increases in the stroke of a brake lever or pedal which, in turn, may cause a malfunction of the brake. A problem also arises when the angle of rotation of the cam departs from the upper limit of a normal range, since the brake may then operate insufficiently or not at all. Further, since the angle of rotation of the cam and hence the point of application thereof varies even in a normal range due to repeated adjsutment, difficulties may occasionally be encountered in keeping the operation of the brake constant depending upon the braking action of the brake arm.
The present invention provides solutions to the above-mentioned problems the prior art offers.
A main object of the present invention is therefore to provide an automatic braking-gap adjuster system for a mechanical drum brake, which always keeps a braking-gap constant in an automatic manner, maintains the angle of turning of a brake arm at a preset value even upon adjustment, is in stable and sure operation due to no change in the stroke of a brake lever or pedal, is simple in construction and is inexpensive to manufacture.
According to the present invention this object is achieved by provision of an automatic brake-gap adjuster system for mechanical drum brakes, comprising a pair of brake shoes, each having one end pivotally supported on a back plate and the other free end adapted to be expanded into engagement with the inner periphery of a brake drum; a cam member rotatably disposed through said back plate between said free ends of said pair of brake shoes and adapted to be rotated by a brake arm; cam collars adapted to take abutment onto said free ends of said brake shoes and mounted on said cam member in such a manner that said collars are rotatable with said cam member, slidable toward a cam shaft and movable in the expanding direction of said brake shoes; and an actuating member threaded into said cam member to take abutment onto the end faces of said collars, thereby moving said collars; and an adjusting member adapted to rotate said actuating member in response to the abrasion of said brake shoes, thereby threadedly moving said actuating member toward said cam shaft, whereby said cam collars are slidingly moved toward said cam shaft in the expanding direction of said brake shoes to expand said brake shoes, so that a brake-gap between the inner periphery of said brake drum and said brake shoes is adjusted.
Another object of the present invention is to provide an automatic brake-gap adjuster system for mechanical drum brakes, which is particularly applicable to a mechanical drum brake of small size by reducing the width of the cam portion of a cam member. The system improves the return properties of brake shoes upon release of braking, reliably transmits the rotational force of the cam member from cam collars engaged with shoe-engaging portion formed on the opposite surfaces of the cam member to shoe webs with no loss, and adjusts the stretching of a brake wire, which may take place due to repeated braking.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which the cam portion of said cam member is provided with a pair of opposite surfaces which the shoe web free ends of said brake shoes face, said opposite surfaces including shoe-engaging portions which are axially provided with cam collar grooves having tapering bottoms at positions symmetrical about the center of said cam shaft, said cam collars taking abutment onto said free ends are slidably fitted into said grooves in such a manner that they extend to move apart said brake shoes, and said actuating member being threadedly moved by said adjusting mechanism to extend said cam collars in the expanding direction of said brake shoes.
A further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which prevents misarrangement of cam collars and is assembled with ease and efficiency.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which said cam collars are formed of symmetrically polygonal plates each including shoe web-contacting surfaces and actuating member-contacting surfaces which intersect at right angles in symmetrical positions, an angle at which said shoe web-contacting surfaces intersect being acute, while an angle at which said actuating member-contacting surfaces intersect being obtuse.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for mechanical drum brakes, which permits cam collars to expand brake shoes from the direction normal to a line drawn by connecting the center of a brake drum with the center of a cam shaft, thereby urging them against the drum brake, so as to surely receive braking torques and prevent local loads from being applied on cam collar grooves for supporting the cam collars, whereby the sliding portions of the collars and grooves are not damaged so that sliding movement of the cam collars is smooth and the efficiency of adjustment is improved.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which the cam portion of said cam member is provided with cam collar grooves into which said cam collars are fitted, said grooves being designed to be inclined at a right angle with a line drawn by connecting the center of said cam shaft with the center of said brake drum during braking.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which prevents powders resulting from wearing, sand, etc. from entering between the head of an actuating member and the end of a cam portion and cam collar grooves to assure smooth rotation of the actuating member and smooth movement of cam collars in the adjusting direction for proper adjustment.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which is further included a cam cover comprising a ceiling for covering the end of the cam portion of said cam member and the ends of said cam collars and skirts formed with cut-outs for permitting movement of said cam collars in the expanding direction of said brake shoes, said cover being mounted on the cam portion of said cam member in such a manner that it is slidable in response to threaded movement of said cam member, with its ceiling being interposed between the end of the cam portion and the head of said actuating member.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which prevents an actuating member which gives a push on cam collars for adjustment of a brake-gap from abutting upon the free ends of brake shoes upon completion of adjustment, thereby restraining said brake shoes against expansion, prevents an adjusting gear for rotating the actuating member from being pushed out a cam member due to threaded movement of the actuating member, so that an adjusting mechanism suffers no damage or failure, and, upon linings reaching the critical abrasion value, indicates the time for replacement of brake shoes by causing an increase in the stroke of a brake lever or pedal.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which the cam portion of said cam member is provided with surfaces which the shoe web free ends of said brake shoes face, said surfaces having a length greater than the thickness of said free ends in the direction of said cam shaft, and in which the head of said actuating member is caused to abut upon the front end of said cam portion to place upon the movement of said actuating member a limitation which defines the critical value of brake-gap adjustment.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which is easy to locate a position at which resilient pawls mate with an adjusting gear as compared with the prior art system according to which a dust cover or back plate is clamped in place at two points, diminishes a chance of misarrangement of parts, and provides smooth and reliable adjustment due to less variations in the loads applied on the adjusting gear.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which said adjusting mechanism comprises an adjusting gear formed integrally with or separately from said actuating member inserted into said cam member and an adjusting lever mounted on a stationary member and adapted to mate with said adjusting gear to rotate said gear in the adjusting direction in response to the abrasion of said brake shoes. and in which said adjusting lever is fitted over the cam shaft of said cam member so as to rotate said cam member, and has its end clamped on said back plate with a dust cover which covers said adjusting gear, and a resilient pawl is engaged with said adjusting gear in such a manner that it is rotatable in the adjusting direction.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which permits rotation of a feed pawl means with the cam shaft of a cam member with no loss, so that the feed means is properly fed for reliable adjustment of a brake-gap and constantly given braking, and allows easy and reliable manufacturing and assembling of the feed pawl means.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which the cam shaft of said cam member is provided around its rear end with axially engaging portions, and a feed pawl means is inserted over the said cam shaft, having therein an opening the edge of which is formed with pieces to be engaged with said axially engaging portions, said feed pawl means being formed around its outer edge with resilient pawls adapted to mate with said adjusting gear, thereby providing rotational feeding of said adjusting gear in the adjusting direction.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which eliminates a disadvantage, as encountered in the prior art, that the degree of wearing of brake linings is not detected until an alarm is given when the abrasion of linings reaches the critical value, in other words, visually detects the degree of wearing of linings, and is simple in construction and inexpensive to manufacture.
According to the present invention, this object is achieved by provision of the above-mentioned system, in which said adjusting gear is formed with spiral guide means, said dust cover adapted to cover said adjusting gear is formed therein with a window, and an indicator means is slidably disposed within said window, the projection of said indicator means being slidably engaged with said spiral guide means, whereby said indicator means is slidable along said window in response to the rotation of said adjusting gear.
A still further object of the present invention is to provide an automatic brake-gap adjuster system for a mechanical drum brake, which prevents effectively an amount heat in braking from being transmitted to an adjusting mechansim, i.e., prevents the adjusting mechanism from being affected by said heat, by disposing the adjusting mechanism outside of a back plate and spaced far away from brake shoes and forming an air passage between the back plate and the adjusting mechanism, and prevents entrance of dust, sand and earth, mud, water, etc. into the adjusting mechanism, whereby reliable adjustment is assured for longer periods of time.
According to the present invention, this object is achieved by provision of an automatic brake-gap adjuster system for a mechanical drum brake, which comprises a pair of brake shoes disposed on the inside of a back plate; a mechanism for expansion of said brake shoes interposed between the shoe web free ends of said shoes and comprises of a cam member rotatably inserted through said plate, cam collars adapted to be slidable toward a cam shaft along said cam member and moved in the expanding direction of said brake shoes, and an actuating member threaded into said cam member and adapted to be moved toward said cam shaft to push said cam collars; and adjusting mechanism adapted to move said actuating member toward the end of said cam member extending out of said back plate in response to the abrasion of brake linings; and a covering mechanism adapted to close tightly said adjusting mechanism with an air passage between said back plate and said adjusting mechanism.